1. Field of the Invention
The present invention relates to pilot control relay valves. Even more particularly, the present invention relates to pilot control relay valve employed to change the directional flow of fluids to a piston, a valve or the like wherein controls provide a fluid signal to drive an end device such as a chemical injection pump to inject chemicals at a slow or rapid rate over a long period of time.
2. General Background
Various devices are known which attempt to control a reciprocating pump. Devices of one such type are used in attempting to control a glycol pump which controls the level of liquid in a gas-liquid system and for circulating liquid in a gas-liquid system. These devices require a separate pump and pilot assembly such as that illustrated in U.S. Pat. No. 2,990,910, issued to G. O. Kimmell and entitled "Apparatus And Method For Circulating Controlling Liquids And Gas-Liquid Systems." Problems arise in the use of this type of system in that it simultaneously relieves pressure on the output or "low" side and increases pressure on the input or "high" side thereby preventing the pump from reaching a low speed or pumping rate.
Other pilot control relay valves rely on springs for the back stroke of the actuating piston in the pump which can lead to fatigue and breakdown.
For a pilot control valve having first and second elongated valve members coaxially and independently longitudinally shiftable within a valve body which overcomes these problems see my U.S. Pat. No. 4,593,712 entitled "Pilot Control Valve" which issued on June 10, 1986. Movement of the first valve member from a first lower position to a second higher position allows supply fluid to act on the second valve for causing it to move from a first lower position and follow the movement of the first valve member. The upward following motion of the second valve member to a second higher position communicates supply fluid to a piston included with the injection pump for causing the piston to be returned longitudinally downward. Thereafter supply fluid is communicated to the first valve member so that the first valve member is returned from its upper position to its lower position. During downward motion of the first valve member, supply fluid is communicated to the second valve member for causing it to move from its second position and follow the movement of the first valve member to its first position. As the second valve member returns to its first position, control fluid is communicated to the piston of the injection pump for causing it and an attached rod to move longitudinally upward, allowing the upward motion of the rod to cause the movement of the first valve member from its first lower position to its second higher position, allowing the process to be repeated.
Therefore, it is a object of the method and apparatus of the present invention to provide a pilot control valve that is powered by supply fluid and which is controlled by the same fluid and which by varying the pressure of the control fluid, the pumping rate is selectable between a low pumping rate and a high pumping rate.
It is a further object of the present ivention to provide a pilot control relay valve without any springs, nuts, bolts or other components which may fatigue or fail under fluid pressure.
It is also an object of the present invention to provide a piolt control valve having a valve member which is shiftable between first and second positions by the control fluid to control the pumping rate. Accordingly, it is a further object of the present invention to provide a pilot control relay valve without a first elongated valve member and a second following elongated valve member which follows the movement of the first valve member and which are coaxially and indpendently longitudinally shiftable and which does not require the second following elongated valve member to communicate supply fluid to move a main piston from a first position to initiate movement of the first valve member from a first position to a second position and which after the movement of the first and second elongated valve members to their second position thereby communicates supply fluid to return the piston to its first position and communicates supply fluid to initiate movement of the first valve member to its first position, thus communicating supply fluid to the following valve member for returning it to its original position, whereby the operation is repeated again and again.
In accordance with this object, it is a further object of the present invention to provide a sealing arrangement which allows control fluid to equalize and bypass in one direction while allowing the control fluid to exert a force on the valve member in the opposite direction.
These objects together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation of the invention and is more fully hereinafter described and claimed.